1. Field of the Invention
The present invention relates to a keyboard device for an electronic keyboard instrument, such as an electronic piano.
2. Description of the Related Art
Conventionally, as a keyboard device for an electronic piano, there has been known one disclosed e.g. in Japanese Patent Laid-Open Publication No. 2002-116760 filed by the present applicant. The keyboard device comprises a plurality of swingable keys, a plurality of hammers provided in association with the respective keys for pivotal movement in accordance with key depression, and a hammer rail for pivotally supporting the hammers. Each of the hammers is formed into an arm-like shape extending in the front-rear direction of the keyboard device, and has a rear end thereof formed with a shaft hole having a C shape in side view and a lower surface thereof provided with an adjustment screw at a location immediately forward of the shaft hole. The hammer rail is formed by a single extrusion molded article of aluminum and extends in the left-right direction over the entire length of all the hammers.
The hammer rail has a hammer supporting part extending vertically, a stopper mounting portion extending obliquely forward and upward from the upper end of the hammer supporting part, and a fulcrum shaft portion projecting forward from the upper portion of the hammer supporting part, and these are formed into one piece. The stopper mounting portion has a front end thereof provided with a stopper for restricting the upward pivotal movement of each hammer and a key switch for detecting key depression information on each key. The key switch comprises a printed circuit board and a plurality of switch bodies attached to the printed circuit board in association with the respective keys. Each of the switch bodies is formed by a rubber switch having a plurality of movable contacts.
In the keyboard device configured as above, the shaft hole of each of the hammers is engaged with the associated fulcrum shaft portion of the hammer rail, whereby the hammer is pivotally supported by the hammer rail, with its adjustment screw placed on the rear end of the upper surface of the associated key. On the upper surface of each of the hammers, an actuator portion for pressing the associated switch body is formed at a location immediately forward of the shaft hole. In a key-released state, the actuator portion is opposed to the switch body with a slight gap. When the key is depressed in this state, the hammer is pushed up by the rear end of the key in accordance with the key depression to be pivotally moved upward about the fulcrum shaft portion. Then, the hammer comes into abutment with the stopper, whereby further pivotal movement of the hammer is stopped. During the pivotal movement of the hammer, the actuator portion of the hammer sequentially presses the movable contacts of the switch body, and a tone generated based on key depression information detected by the switch body is output from speakers of the electronic piano.
As another keyboard device for an electronic piano, there has been known one disclosed e.g. in Japanese Utility Model Registration Publication No. 2550102 filed by the present applicant. This keyboard device includes a keyboard chassis formed by two front and rear chassis (i.e. a front chassis and a rear chassis) each extending in the left-right direction of the keyboard device, and a plurality of metal reinforcement beams each extending in the front-rear direction and arranged in the left-right direction in a manner spaced from each other, so as to connect the two front and rear chassis, and a plurality of keys supported from below by the keyboard chassis and arranged side by side in the left-right direction.
A keyframe front and a keyframe center each extending in the left-right direction are rigidly secured to the respective front and rear portions of the front chassis of the keyboard chassis. On each of the keyframe front and the keyframe center, a plurality of front pins and balance pins are erected and arranged side by side in the left-right direction. Each of the keys has a front end thereof formed with a front pin hole open downward for engagement with the associated front pin, and a central portion thereof formed with a balance pin hole through which the associated balance pin is engaged. Thus, the key is supported on the keyframe center such that the key can swing about the balance pin in a state where the front pin prevents the key from swinging laterally.
In the keyboard device disclosed in Japanese Patent Laid-Open Publication No. 2002-116760, the pivotal speed, position, etc. of a hammer are determined according to the strength and depth of key depression by a player, and key depression information is detected based on the speed and amount of pressing of the switch body by the hammer. In order to detect the key depression information properly, it is required to set the positional relationship between the hammers and the key switch with high accuracy. Further, to fulfill this requirement, high dimensional accuracy is demanded of the hammer rail that supports the hammers and has the key switch mounted thereon.
However, in the above-described keyboard device, since the hammer rail is formed by an extrusion molded article of aluminum, the demanded high dimensional accuracy cannot be sufficiently obtained. More specifically, the hammer rail has its cross-section formed relatively accurately, but variation due to warpage or distortion can occur particularly in the fulcrum shaft portion having a small cross-section and extending long in the left-right direction. In this case, even if the variation is minute (e.g. 0.1 mm or so), proper relationship between the hammer engaged with the fulcrum shaft portion and the associated switch body of the key switch mounted to the stopper mounting portion may not be obtained. In this case, proper key depression information cannot be obtained, which makes it impossible to ensure proper tone generation.
In the case of the keyboard device configured as disclosed in Japanese Utility Model Registration Publication No. 2550102, when the length of a key is to be changed e.g. following a design change of an electronic piano, by achieving commonality of each of the front chassis, the rear chassis, the keyframe front, and the keyframe center, between before and after the design change, and then manufacturing the metal reinforcement beams for connecting the two chassis according to the length of the key, it is possible to suppress an increase in manufacturing costs due to the design change. However, in this keyboard device, the keyframe front and the keyframe center are rigidly secured to the front chassis, and hence the distance between the front pin hole and the balance pin hole of each key is determined depending on the distance between the keyframe front on which the front pins are erected and the keyframe center on which the balance pins are erected. For this reason, e.g. as to the length of a portion of the key extending forward from the swing fulcrum of the key, an allowable range of setting is limited within the dimension of the front chassis in the front-rear direction, and therefore the degree of freedom in designing the keyboard device is not large enough.
Further, the surroundings of the keyframe center rigidly secured to the front chassis is supported from below by the metal reinforcement beams, but between adjacent two of the metal reinforcement beams, the front chassis is spaced from the keybed on which the keyboard chassis is placed. For this reason, when an impact is applied to the keyboard device e.g. due to careless dropping of the electronic piano during transportation of the same, a portion of the front chassis between the adjacent metal reinforcement beams around the keyframe center can be warped downward, resulting in permanent deformation thereof. In this case, a key supported by the keyframe center at a location corresponding to the warpage is lowered in level with respect to the other keys, which makes the keys irregular in level. Further, when the key is depressed strongly, the keyframe center can be vibrated vertically. In this case, key touch feeling is degraded. Thus, the above-described keyboard device leaves room for improvement.